The present invention relates to improved weft feeler unit for a fluid-jet loom, and more particularly relates to improvement in the construction of a weft feeler unit which includes, as a detection terminal, a weft feeler made up of a pair of electrodes mounted to the weft arrival side end of a reed on a fluid-jet loom such as a water-jet loom.
It is a usual practice on a fluid-jet loom to arrange a weft feeler on the reed at a position where a normally inserted weft arrives. At every beating, the weft feeler detects the presence of the weft at that position and generates either a normal or an abnormal signal for every weft insertion. The normal signal indicates that the weft in that cycle has been inserted correctly (normal weft insertion) and that the loom should continue running. The abnormal signal indicates that the weft in that cycle has not been inserted correctly (abnormal weft insertion) and that the loom should stop running. These signals are passed to the drive control unit of the loom. One typical example of such a weft feeler unit is disclosed in Japanese Patent Opening No. 70163/1977.
It is well known that the electric resistance of a yarn impregnated with fluid such as water is appreciably high. Consequently, it is desirable to apply a high level of voltage to the electrodes composing the weft feeler of the above-described type in order to obtain high rate of accuracy in weft detection. In other words, such high level of voltage is preferably required in order to ensure that a normal signal will be generated without fail when the weft has been correctly inserted and the electrodes have been bridged by the weft. However, use of such a high level of voltage is liable to cause insultation problems. That is, a high level of voltage tends to form an undesired electric bridge between the electrodes due to the presence of yarn fluffs and/or water drops floating in the space between the electrodes. Further, deterioration in insultation eventuates in dielectric breakdown. These accidents tend to cause the generation of a normal signal even when the weft has actually been inserted incorrectly. In order to obviate this problem, it has been conventionally employed to apply electric voltages of about 500 V to the electrodes composing the weft feeler despite the above-described advantage in use of high level of voltage.
When a high twist yarn is used for a weft, the relatively low hydroscopic property and twist torque of the yarn make the weft whip significantly at the position of the weft feeler, thereby causing incomplete contact of the weft with the electrodes composing the weft feeler. Such incomplete contact disables production of signal current of sufficient magnitude with the above-described conventional level of voltage applied to the electrodes.
Further, fluctuation in the signal current is liable to cause detection errors. That is, even when the weft has come into stable contact with the electrodes, the relatively low level of the output signals disables correct discrimination of the signals. Further, the weft in fact whips in most cases upon contact with the electrodes and this inevitably causes a significant fluctuation in level of the output signals. As a consequence, an abnormal signal is generated to stop the running of the loom even though the weft has been correctly inserted. This naturally results in low rate running efficiency of the loom.